Nitrogen and Foliar Zinc Applications Alter Mineral Accumulation and Spatial Distribution in Maize Kernels Along the Ear of Contrasting Genotypes

Elucidating the spatial distribution of mineral nutrients within maize ears is important for improving both grain yield and nutritional quality. A five-year field study was conducted in the North China Plain to investigate how soil N and foliar Zn applications influenced grain yield and nutrient distribution among kernel positions within the maize ear. Ten maize cultivars were initially screened for responsiveness to foliar zinc, and two contrasting cultivars, Zhengdan 958 (zinc-responsive) and Longping 638 (zinc-low-responsive), were selected for detailed evaluation under three N application rates, with or without foliar Zn application. Nutrient concentrations of N, P, K, Cu, Mn, Fe and Zn were highest in basal kernels and declined toward the upper ear, with their accumulation represented as basal > middle > upper. Increasing N rates enhanced grain yield and total mineral accumulation and altered nutrient partitioning within the ear. A total of 225 kg N ha−1 increased Zn concentration in the upper kernel but decreased in the basal kernel, while increased proportions of N, Mn and Zn accumulated in the basal kernel but decreased in the middle kernel, relative to 180 kg N ha−1. Foliar Zn significantly reduced barren tip length, increased Zn concentration and accumulation, and decreased P concentration but had little effect on nutrient distribution among ear positions. Strong positive relationships were observed between mineral concentrations in whole-ear grain and those in individual ear positions. Thus, N and Zn management could influence maize yield and grain mineral nutrition allocation among ear positions, providing new insights into enhancing the mineral nutritional quality of maize grain.